Low profile cam-in socket having terminals engaging a rib

Abstract: A socket for electrically connecting a circuit panel (14) to a substrate comprises an an insulative housing (10) defining an elongated slot (12) for receiving the circuit panel (14). A plurality of terminal receiving cavities (16) are spaced apart along a length of the slot, and each of the cavities is open to the slot on opposite sides (22, 24) thereof. The housing (10) includes a rib (20) extending beneath the slot along its length. A plurality of electrically-conductive terminals (30) are disposed in respective ones of the cavities (16). Each of the terminals (30) comprises an integral body including a housing engaging section (32) having opposed surfaces (34, 36) each gripping a respective opposite side (46, 48) of the rib (20). Each terminal has a lead (58) extending to an exterior of the housing (10) for electrically engaging a substrate, and a pair of resilient contact arms (52, 62) extending into the slot (12) from respective opposite sides of the slot (12) for electrically engaging opposite sides of the circuit panel (14).

Description: The invention relates to a socket for electrically interconnecting circuit panels, and more particularly, to a housing and terminals for a cam-in socket wherein the terminals are retained in the housing by gripping opposite sides of a rib of the housing, thereby providing a low profile socket. A single in-line memory module (SIMM) presents a high density, low profile single in-line package for electronic components such as dynamic random access memory integrated circuit components. Each module comprises a plurality of integrated circuit components mounted on a circuit panel card having contact surfaces adjacent one edge. A plurality of these circuit panels, or daughtercards, can then be mounted on a circuit board mothercard. Sockets known as SIMM sockets are well known to receive the edge of a circuit panel daughtercard and establish an electrical interconnection with a circuit board mothercard. U.S. Patent No. 4,946,403 discloses a SIMM socket which permits a circuit panel to be inserted into the socket with a low insertion force. This patent also discloses a right angle SIMM socket for mounting the daughtercard parallel to the mothercard in order to reduce overall height of a packaged daughtercard/mothercard assembly. A problem with right angle mounting is that the mothercard must have a relatively large surface area to accommodate a plurality of daughtercards. U.S. Patent No. 5,041,005 discloses a low profile SIMM socket which permits mounting a daughtercard at an angle such as twenty-five degrees relative to the mothercard. This socket permits a plurality of daughtercards to be mounted in parallel side by side relationship while still providing a relatively low overall height for the packaged assembly. In order to achieve a still denser array of daughtercards on a mothercard, it would be advantageous to narrow the SIMM sockets in order that they could be mounted on the mothercard in closer parallel relationship. Width of the sockets is primarily limited by the profile of the terminals which must be housed therein. Each of the above-reference patents discloses a socket housing having a central rib which extends beneath a panel receiving slot along a length of the housing. The patents disclose terminals which are retained in their respective socket housings by two separate and spaced apart retention elements, one of the elements engaging on the central rib, and the other of the elements engaging an inner surface of an outer wall of the housing. Width of the sockets could be reduced if the terminal retention elements were localized so as to engage only one portion of the socket housing, in particular, the central rib. EP-A-0 419 818 discloses a low insertion force socket for connecting a daughtercard to a mothercard in perpendicular relationship. The socket has terminals disposed in cavities of an insulative housing. The cavities are spaced apart along opposite sides of a slot in the housing for receiving the edge of the daughtercard, each terminal comprising preloaded spring arms located in the cavities for establishing contact with the daughtercard. Each terminal is an integral body and includes a housing engaging section defining a slot for gripping a rib extending beneath the slot along the length thereof and retaining the terminal in position. With the exception of EP-A-0 419 818, which relates to a straight entry connector, the above-referenced patents also disclose cam-in sockets wherein a daughtercard is inserted into the socket at a first angle relative to the mothercard, the insertion being resisted by a zero or low insertion force. The daughtercard is then rotated to a second angle relative to the mothercard, the rotation being resisted by spring portions of the terminals which are designed to provide a relatively low resistance to the rotation. Each of the terminals has two contact portions for engaging opposite sides of the daughtercard. One of the contact portions is disposed on a substantially cantilever spring arm, and the other of the contact portions is disposed on a substantially C-shaped spring arm. Each of the spring arms must have a low spring rate in order to provide a fairly uniform normal force on different daughtercards having a thickness tolerance which varies over a relatively wide range. The C-shaped spring arm has multiple flexuous sections along its length and therefor has an inherently lower spring rate than the cantilever spring arm which has only one flexuous section at its root. It would be advantageous for the terminal to have contact portions on a pair of curved spring arms having low spring rates so that the socket would be more tolerant of variations in daughtercard thickness. The present invention consists in a low profile socket for electrically connecting a circuit panel to a substrate, comprising an insulative housing having an elongated slot arranged for mounting the circuit panel in inclined relation to the substrate, a plurality of terminal receiving cavities spaced apart along the slot, each of the cavities being open to the slot on opposite sides thereof, a plurality of electrically conductive terminals respectively disposed in the cavities, and a rib extending beneath the slot along the length thereof, each of the terminals being an integral body including housing engaging means, a lead extending to an exterior of the housing for electrically engaging the substrate, and a pair of resilient contact arms extending into the slot from opposite sides of the slot for electrically engaging opposite sides of the circuit panel, characterised in that the housing engaging means of each terminal is formed by a section of the integral body defining a slot having opposed surfaces gripping opposite sides of the rib, and neither of the contact arms is preloaded against the rib, whereby contact portions of the contact arms avoid picking up smears of plastic from the rib as the terminal is inserted into the housing. An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings in which:- Fig. 1 is a perspective view of a socket according to the invention. Fog. 2 is an exploded cross-sectional view of a housing and terminal for a socket according to the invention. Fig. 3 is a perspective view of a terminal for the socket according to the invention. Fig. 4 is a cross-sectional view of the socket having a terminal disposed therein. Fig. 5 is a cross-sectional view of the socket taken along line 5-5 of Fig. 1, and a circuit panel in an initial position during insertion into the socket. Fig. 6 is a cross-sectional view of the socket having a circuit panel disposed in a final position therein. As shown in Figs. 1 and 2, a socket according to the invention comprises an insulative housing 10 which is preferably made from a plastic such as glass reinforced liquid crystal polymer. The housing 10 has an elongated slot 12 dimensioned to receive a circuit panel 14. A plurality of terminal-receiving cavities 16 are spaced apart along a length of the slot 12. The cavities 16 extend perpendicular to the slot 12 through an interior of the housing 10, each of the cavities 16 being open to the slot 12 through opposite sidewalls 22, 24 of the slot 12, wherein terminals disposed in the cavities 16 can communicate through the interior of the housing 10 between opposite sides of a circuit panel 14 disposed in the slot 12. The housing 10 includes a rib 20 that extends beneath the slot 12 along the length of the slot. The rib 20 is preferably centrally located beneath the slot 12 with a top surface of the rib 20 defining at least a portion of a floor 26 of the slot 12. The rib 20 has opposite sides 46, 48 that are exposed within each of the cavities 16. A plurality of electrically-conductive terminals 30 are disposed in respective ones of the cavities 16. The terminals 30 are inserted into the cavities 16 from a bottom of the housing 10 as shown in Fig. 2, preferably by automatic insertion machinery. As shown in Figs. 2 and 3, each of the terminals 30 comprises an integral body that is preferably edge-stamped from a blank strip of phosphor bronze material. The terminal body includes a housing engaging section 32 that defines an upwardly-open slot 40 which receives the rib 20 of the housing 10. Surfaces of the slot 40 define opposed gripping surfaces 34, 36 which are spaced apart at a distance selected to be narrower than a width of the rib 20. Forceful insertion of the terminal 30 into the housing 10 causes the gripping surfaces 34, 36 to spread further apart as the rib 20 enters the slot 40, whereby the rib 20 becomes frictionally engaged between the gripping surfaces 34, 36. In a preferred embodiment, one of the gripping surfaces 34 includes a barb 42 which digs into the plastic of the rib 20 so as to firmly secure the terminal 30 in the cavity 16. The other gripping surface 36 is a planar surface extending perpendicular to a bottom planar surface 38 of the slot 40. The planar surfaces 36 and 38 abut respective planar surfaces 44 and 48 of the rib 20 when the terminal is fully inserted in the cavity 16 as shown in Fig. 4, thereby locating the terminal 30 with respect to the slot 12 in the housing 10. According to the invention, each of the terminals 30 has a pair of resilient contact arms 52, 62 which extend from fixed origins 53, 63, respectively, near the housing engaging section 32, to free ends 55, 65, respectively. The contact arms 52, 62 extend into the slot 12 through respective opposite sidewalls 22, 24 of the slot 12 so that circuit panel engaging portions of the arms 52, 62 may engage circuit traces on opposite sides of a circuit panel 14 when the circuit panel is inserted into the slot. In the preferred embodiment shown in Figs. 2 and 3, each of the contact arms 52, 62 has a substantially C-shaped curved profile that extends from its respective fixed origin 53, 63 to a highest portion 54, 64 and thence downwardly to its respective free end 55, 65 which defines the circuit panel engaging portion of the contact arm. Every bend of a contact arm provides a flexuous section, i.e., a section that provides flexibility, for the contact arm. The curved profile of each contact arm 52, 62 defines a plurality of flexuous sections which result in each contact arm having a spring rate that is lower than the spring rate of a simple cantilever beam having the same overall length as that contact arm. Thus, the contact arms 52, 62 are provided with relatively low spring rates in a minimum size package. The low spring rates enable the socket to accept different circuit panels 14 having a thickness which varies over a relatively wide tolerance range because the range of normal forces encountered by the different thicknesses of circuit panels is kept to a minimum. Either of the contact arms 52, 62 may further include additional curved sections such as S-bend section 57, thereby providing further resilience for the contact arm and a further lowering of its spring rate. Each terminal 30 further includes a lead 58 which extends to an exterior of the housing 10 when the terminal 30 is disposed therein as shown in Fig. 4, the lead 58 being engageable with respective circuit traces on a substrate 18 such as a circuit board. The lead 58 may be of the post type (shown) which registers in a plated through-hole in the substrate 18. Alternatively, the lead 58 may include a foot (not shown) for surface mounting on a contact pad of the substrate 18. In any event, the contact arms 52, 62 and the lead 58 enable each terminal 30 to provide an electrical interconnection between associated circuit traces on the circuit panel 14 and the substrate 18. As shown in Fig. 5, a circuit panel 14 is inserted into the slot 12 at an insertion angle wherein the circuit panel enters freely between free ends of the contact arms 52, 62 and encounters little or no resistance to insertion. The circuit panel 14 is then rotated to a final position in the direction of the arrow shown in Fig. 6. During the rotation, the circuit panel 14 functions as a lever to cam the contact arms 52, 62 at least partly beyond the slot 12 and into the cavity 16 against a resistance offered by the resilient contact arms. Also during the rotation, circuit panel engaging portions at the free ends 55, 65 slide on contact traces (not shown) of the circuit panel 14, thereby wiping the contact surfaces clean. A socket according to the invention has the advantage that the terminals 30 are retained in the housing 10 by two retention elements (gripping surfaces 34, 36) which are localized at the housing engaging section 32 and which engage opposite sides of a single element of the housing 10, i.e., the rib 20. The rib 20 may be relatively narrow and, since no side wall of the housing 10 is engaged by the terminal 30, the housing 10 can be made narrower than previously possible, thereby providing a low profile socket. Further, the invention provides a socket wherein the contact arms 52, 62 have low spring rates, but neither of the contact arms is pre-loaded against the rib 20 as is common in the prior art sockets. The invention thus eliminates a problem wherein a circuit panel contacting portion of the contact arm picks up a smear of plastic from the rib 20 as the terminal is inserted into the housing, which smear of plastic could prevent good electrical contact of the contact arm with a circuit panel inserted received in the socket.

Claims: A low profile socket for electrically connecting a circuit panel (14) to a substrate (18), comprising an insulative housing (10) having an elongated slot (12) arranged for mounting the circuit panel in inclined relation to the substrate, a plurality of terminal receiving cavities (16) spaced apart along the slot, each of the cavities being open to the slot on opposite sides thereof, a plurality of electrically conductive terminals respectively disposed in the cavities, and a rib (20) extending beneath the slot along the length thereof, each of the terminals being an integral body including housing engaging means (32), a lead (58) extending to an exterior of the housing for electrically engaging the substrate, and a pair of resilient contact arms extending into the slot from opposite sides of the slot for electrically engaging opposite sides of the circuit panel, characterised in that the housing engaging means of each terminal is formed by a section (32) of the integral body defining a slot (40) having opposed surfaces (34,36) gripping opposite sides of the rib (20), and neither of the contact arms is preloaded against the rib (20),whereby contact portions of the contact arms avoid picking up smears of plastic from the rib (20) as the terminal is inserted into the housing. The socket according to claim 1, wherein the rib (20) is centrally disposed beneath the slot (12). The socket according to claim 1 or 2, wherein a surface of the rib (20) defines at least a portion of a boundary wall (26) of the slot (12). The socket according to claim 1, 2 or 3, wherein each of the contact arms (52,62) has a profile that extends from a fixed origin (53,63) upwardly to a highest portion and then downwardly to a circuit panel contact portion. The socket according to claim 1, 2, 3 or 4, wherein each of the contact arms (52,62) has a profile that defines at least two bends. The socket according to claim 5, wherein each of the contact arms (52,62) is substantially C-shaped. The socket according to any preceding claim, wherein one of the opposed surfaces (34,36) of the housing engaging section includes a barb (42).

Inventors: KINROSS TIMOTHY JAMES, THRUSH ROBERT LEE, KINROSS, TIMOTHY JAMES, THRUSH, ROBERT LEE
Applicants: WHITAKER CORP, THE WHITAKER CORPORATION
Application year: 1994
Main classification: H01R12
IPC codes: H01R12